The present invention relates generally to a digital control system, such as automotive engine control system, anti-skid brake control system or the like, which includes a monitor system operative upon starting system operation to check power supply, indicators and so forth. More particularly, the invention relates to an initialization-responsive monitor system for checking the operating conditions of the digital control system in response to initialization, which monitor system distinguishes whether or not initialization has taken place in response to turning ON of the system, i.e. a socalled "cold start", and performs monitor operations only in response to a cold start.
In recent years, digital processor systems for controlling various automotive vehicle components, such as engines, brake systems, air conditioner systems, height regulators and so forth have become widely available. Many such systems are provided with selfcheck functions and initial-reset functions upon starting system operations. Such functions are essential for preventing the system from malfunctioning. The control systems are further provided watch-dog timers or equivalent components which monitor for program errors in the control system. A watch-dog timer generally checks output signals periodically produced by the control systems and produces an error signal when the interval between system output signals becomes longer than a predetermined period. When an error signal is issued by the watch-dog timer, the control system is re-initialized in order to fail-safe the system. Such a fail-safe system has been disclosed in the U.S. Pat. No. 4,363,092, issued on Dec. 7, 1982 to Toshimi ABO et al and commonly assigned to the assignee of the present invention.
U.S. Pat. No. 4,363,092 discloses a malfunction preventing system for a microcomputer system, which detects an abnormal condition in the program execution to produce an alarm or reset signal to automatically restart the computer. Program run signal is detected in checking the microcomputer operation by measuring intervals of the program run signal. Since the program run signals are to be derived at predetermined time intervals when the microcomputer is running under normal condition, judgement can be made that the microcomputer is in failure when the interval of the program run signals is longer than a given period of time.
Further, the digital control system may be provided with a self-monitor system for checking actuators to be controlled, monitor indicator or display and so forth upon the system is reset and initialized. This self-monitor system generally applies damy loads to the acutators and indicator to testingly operate them, In case of the digital control systems applied to the vehicle, problem is arisen that, if initialization is taken place due to failure of program run signal in a given period of time during the vehicle running, self-monitor operation is taken place to actuate the actuators. When the digital control system is applied for engine control, the engine will be driven irrespective of driving condition to degrade drive feeling. In worst case, the engine will stall while the vehicle is running. On the other hand, when the digital control system is applied for an anti-skid brake control system, a pressure control valve in a hydraulic brake circuit may be placed at release position to disable application of brake while the damy load is applied to the actuator.
Further, by turning ON the monitor indicator or indicators, the drive must fear if the digital control system per se or acutator thereof is in deed damaged.